Influence of Ga content and high temperature annealing on the short range order and magnetostriction of Fe–Ga single crystals

Large magnetostriction observed in Fe–Ga alloys makes them a very important class of alloys for use in a wide range of actuation and sensing applications. This study of quantitative measurements of short-range order (SRO) in a series of Fe–Ga alloys provides valuable insights into the correlations of magnetostrictive responses with an increase in the Ga concentration and annealing. A quantitative assessment of SRO in the first seven shells around an atom in as-grown and high-temperature annealed [001]-oriented Fe–Ga alloy single crystals with Ga contents in the range of 5–20 at. % was carried out using the diffuse peaks in the forbidden (100) peak region of the θ–2θ high-resolution x-ray diffraction pattern. The SRO parameter values obtained indicate that very little short-range ordering occurs in Fe–Ga alloys with low Ga concentrations and ordering is limited to the first few shells. With an increase in Ga content, SRO increases with ordering occurring out to further shells. High temperature annealing decreases SRO parameters to levels approaching random solid solution. The decrease in short-range ordering with high-temperature annealing correlates with the increase in magnetostriction and confirms the hypothesis that the difference in the extent of ordering is the source of the observed high sensitivity of magnetostriction to changes in thermal history.